Go (golang) WebAssembly (WASM) hello world example

main.go

package main

import (
	"syscall/js"
)

// Add ...
func Add(a, b int) int {
	return a + b
}

func main() {
	c := make(chan struct{}, 0)

	add := func(args []js.Value) {
		go func() {
			js.Global().Set("output", js.ValueOf(Add(args[0].Int(), args[1].Int())))
			close(c)
		}()

	}

	js.Global().Set("add", js.NewCallback(add))

	<-c
}

Makefile

compile:
	GOARCH=wasm GOOS=js go build -o test.wasm main.go

copy:
	cp $(go env GOROOT)/misc/wasm/wasm_exec.{html,js} .

serve:
	go run server.go

server.go

package main

import (
	"flag"
	"log"
	"net/http"
	"strings"
)

var (
	listen = flag.String("listen", ":8080", "listen address")
	dir    = flag.String("dir", ".", "directory to serve")
)

func main() {
	flag.Parse()
	log.Printf("listening on %q...", *listen)
	log.Fatal(http.ListenAndServe(*listen, http.HandlerFunc(func(resp http.ResponseWriter, req *http.Request) {
		if strings.HasSuffix(req.URL.Path, ".wasm") {
			resp.Header().Set("content-type", "application/wasm")
		}

		http.FileServer(http.Dir(*dir)).ServeHTTP(resp, req)
	})))
}